1. Field of the Invention
The present invention relates to a magnetic recording/reproducing apparatus, such as a floppy disk drive (FDD) or hard disk drive (HDD), for reading data from and writing data to a magnetic medium, and also to a semiconductor integrated circuit device for driving such an apparatus.
2. Description of the Prior Art
A conventional semiconductor integrated circuit device (hereinafter referred to as an LSI) for driving a magnetic recording/reproducing apparatus will be described with reference to FIG. 8. The LSI 70 shown in FIG. 8 has a signal processing circuit 71 for processing the data read from a magnetic medium and for processing the data to be written to the magnetic medium, a control circuit 72 for producing control signals for controlling a spindle motor and a stepping motor that are connected externally, a large current driver 73 for supplying current for controlling the stepping motor in accordance with a control signal produced by the control circuit 72, a clock output terminal 74 for feeding out a clock for controlling the spindle motor from the control circuit 72, a control terminal 75 for feeding out a spindle on/off control signal from the control circuit 72, a test signal terminal 76 for receiving a test signal for establishing a test mode for testing the individual blocks constituting the LSI 70 one by one, output terminals 77, 78, 79, and 80 for feeding out the current supplied from the large current driver 73, a buffer 83 for feeding the signal received at the test signal terminal 76 to the control circuit 72, and buffers 81 and 82 for feeding the clock and the on/off control signal from the control circuit 72 to the clock output terminal 74 and the control terminal 75, respectively. The signal processing circuit 71 is controlled by the control circuit 72.
In general, when such an LSI 70 is checked for defects, its constituent blocks are subjected one by one to functional testing. To achieve this, various test signals corresponding to the test modes for the individual blocks are fed via the test signal terminal 76 to the control circuit 72, and the control circuit 72, recognizing those test modes, conducts testing of one block after another.
On the other hand, in recent years, to cope with the general trend toward miniaturization in magnetic recording/reproducing apparatuses, LSI chips have come to be provided with less and less pins. However, as the above-described conventional example illustrates, to conduct function-by-function testing of an LSI chip, the LSI chip needs to be provided with one to several test pins for receiving test signals that bring the LSI chip into test modes. This requires that an LSI for use in a magnetic recording/reproducing apparatus such as an FDD have 52 or more pins, and has thus been hindering the effort to reduce the number of pins thereof. Moreover, providing extra pins as such test pins inevitably increases the cost of the LSI chip.